Apparatus and method for binocular measurement system

ABSTRACT

An apparatus and method are disclosed wherein a linear array of electromagnetic radiation emitting devices are arranged in association with a moving workpiece. Electromagnetic radiation emitted by the array is received by two or more receivers. Several non-contact measurements may be obtained on a workpiece using the present apparatus and methods.

This application is a continuation of application Ser. No. 08/301,352,filed Sep. 6, 1994, now U.S. Pat. No. 5,546,808.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates generally to measurement systems, and moreparticularly, to non-contact measuring of rolled, calendared, woven,extruded, and other sheet and web products. The invention incorporates aelectromagnetic radiation emitter, a electromagnetic radiation receiver,and a measurement processing unit.

There are many situations in industrial process control where thecontinuous, accurate measurement of product width, thickness, or edgeposition can improve the quality and efficiency of the productionprocess. There are only a few known methods for making some of thesemeasurements. For example, in the primary metals industry, the mostcommon methods involve the use of charge coupled device (CCD) televisioncameras with elaborate mounting devices and expensive computer supportsystems. Other methods involve mechanically scanned laser beams andmechanically positioned opto-electronic devices. The mechanicallypositioned devices generally require frequent maintenance in theindustrial environment while the scanned laser devices also have movingparts that wear out and require unscheduled down time or scheduledperiodic maintenance.

In the CCD camera systems, a small change in the position of the camerais multiplied by the magnification of the lens in such systems. If thelens is focusing the view of a 40 inch wide strip, for example, on to a1 inch long array, a change in the position of the camera of a fewthousands of an inch is multiplied by a factor of 40 as the imageposition shifts on the array. The thermal growth in the length ofmounting fixture support arms must be compensated for if accurateposition measurements are to be made with such a system. Thus, theelaborate fixtures that are required for such systems, and theinstallation and computer support needed, often make the cost of CCDcamera systems prohibitive.

Materials undergoing industrial production processes vary widely inphysical makeup, such as extruded plastics or steel billets. Speed ofmovement of these materials as they are being processed also varieswidely. Some processes may move a work piece at a very slow rate ofspeed while other processes may move a work piece at speeds of upwardsto 90 mph. Some materials will also reach extremely high temperature.This must be taken into consideration where measurement devices couldpotentially be destroyed by such temperatures.

One measurement system which has found substantial acceptance inindustry is marketed under the trademark "SCAN-A-LINE®". TheSCAN-A-LINE® measurement system employs a linear array ofelectromagnetic radiation emitting diodes positioned on one side of amaterial, such as a web or sheet moving within a production process. Thediodes of the array are illuminated in a scanning sequence having astable time base, for example, at a 20 KHZ rate developed by a quartzcrystal oscillator. Positioned above the moving material underproduction and opposite the associated diode array, is a tunedphotoresponsive receiver which reacts to the illumination emanating fromthe diodes which are unblocked or partially blocked from view by thereceiver by the moving material. Associated controls connected to thereceiver are called upon to extrapolate the electromagnetic radiationsignals to develop measurement information concerning the material. Theextrapolation is based upon the observation that each LED in theemitting array produces a cone of electromagnetic radiation, and theelectromagnetic radiation cones from adjacent LEDs overlap in theelectromagnetic radiation path to the receiver. An edge of the productbeing measured blocking the electromagnetic radiation path from theemitting diodes to the receiver will attenuate the electromagneticradiation from more than one diode. The extrapolating process takessamples of the amplitude of the electromagnetic radiation received insequence from the partially blocked and unblocked LEDs, and develops atime-based stair step electromagnetic radiation output patternrepresenting scan across the edge. The edge position of the materialbeing observed may then be defined as the time equivalent point on thesmooth curve signal where the voltage drops to one-half of the peak LEDsignal amplitude. The SCAN-A-LINE® system is marketed by HarrisInstrument Corporation of Columbus, Ohio.

The SCAN-A-LINE® system was first patented in U.S. Pat. No. 5,220,177,which issued on Jun. 15, 1993. The patent described a system whereineach electromagnetic radiation emitting device of the array utilized isenergized by a unique drive current which is preselected to cause theemission of electromagnetic radiation exhibiting substantially uniformintensity at the receiver when there is no attenuation of theelectromagnetic radiation by a material under edge evaluation. Suchbalancing or optimization of the array electromagnetic radiation outputnot only achieves importantly enhanced system accuracy in carrying outedge location, but also substantially expands the range of applicationfor such non-contacting measurement techniques. In this regard, the edgelocating technique can be employed with transparent or semi-transparentmaterials. When so employed, the time based trigger signal from whichedge data is developed in generated at a location in scan time between atransition of detected amplitudes representing a maximum value and aminimum value. System accuracy is substantially improved through theutilization of a receiving photodetector assembly having a lengthwisedimension which is expanded. With the combination of this improvedreceiving approach and the balanced electromagnetic radiation values atthe receiver, system performance has been observed to be improved beyondwhat would have been expected.

Many of today's industrial measurement applications require measurementof width or position of a product having an unstable passline.Measurement of the instability of passlines has gained in importance.Furthermore, measurement of the width of a material work piece and thethickness of the workpiece are of significant importance in today'sindustrial process applications. Through the employment of semiconductordevice based arrays emitting in the infrared region of theelectromagnetic spectrum in conjunction with silicone photocell receivercomponents, substantially expanded stand-off distances and spacingbetween the receivers and emitter, are available. Enhanced spacingpermits improved edge detection of hot materials such as steel billets.The improved ray trace geometry achieved with enhancedemitter-to-receiver spacing achieves enhanced edge location accuracy atthe passline where vertical movement of the material may be encountered.Ray trace geometry further permits an advantageous lower outside edgedetection where the edges of relatively thick material forms such, asbillets of steel, are monitored.

With the apparatus of the present invention, multiple receivers may beemployed with one or more emitters. The receivers may be removed tolocations directly over each end of a strip emitter. This arrangementhelps to eliminate passline errors. In the present invention, preferablytwo receivers are used for each emitter and each receiver is locatedover one of the opposite ends of the emitter. In this manner, a signalcan be developed that represents passline height. The passline heightsignal can effectively be used to correct width measurements for heightchanges. Thus, the present invention is a system of binocular visionmeasurement.

By scanning the electromagnetic radiation emitted from an array in acontrolled sequence, with a workpiece positioned between theelectromagnetic radiation emitting source and at least two receivers,several important measurements can be made concerning the workpiece, asthe workpiece moves through a production process. In accordance with thepresent invention, an array of spaced discrete electromagnetic radiationemitting devices are disposed generally along an array axis. Eachelectromagnetic radiation emitting device is responsive to theapplication of a drive current thereto to emit electromagneticradiation. The electromagnetic radiation array is positioned a selectdistance from one side of a material workpiece and is located to extendoutwardly from at least one edge of the workpiece, At least twophotoresponsive receivers are positioned at a predetermined stand-offdistance from the material workpiece, in electromagnetic radiationreceiving relationship with the array, and oriented so as to position aphotodetector axis in substantially parallel relationship with the arrayaxis as each electromagnetic radiation emitting device is discretelyenergized in a sequence by the application of drive current at apredetermined system frequency. The photodetectors detect theelectromagnetic radiation emitted by the electromagnetic radiationemitting devices which are either partially attenuated or nonattenuatedby the material workpiece. From the electromagnetic radiation detection,the present invention enables the derivation of output signals at thesystem frequency which exhibits amplitude data. By correlating theamplitude data with time and space location data, to derive a signalrepresenting a desired measurement concerning the material workpiece.

The present invention comprises the apparatus and method possessing theconstruction, combination of elements, arrangement of parts and stepswhich are exemplified in the following drawings and detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of one embodiment of an apparatusof the present invention employed to measure a sheet of material;

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1;

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2;

FIG. 4 is a sectional view taken along line 4--4 of FIG. 1;

FIG. 5 is diagrammatic view of an embodiment of the present inventionhaving a single emitter in association with two spaced-apart receivers;

FIG. 6 is a video timing diagram of the embodiment shown in FIG. 5;

FIG. 7 is a diagrammatic view of a video decoder for use in anembodiment of the present invention;

FIG. 8 is a diagrammatic view of an arrangement of the apparatus of thepresent invention for use with a single edge position formula;

FIG. 9 is a diagrammatic view of an arrangement of the apparatus of thepresent invention for use with a workpiece height formula;

FIG. 10 is an electrical schematic diagram of an embodiment of a videopre-processor of the present invention;

FIG. 11 is a diagrammatic view of an arrangement of the apparatus of thepresent invention for use with a workpiece thickness formula where theworkpiece is located directly at the electromagnetic radiation source;

FIG. 12 is a schematic block diagram of video processing of the presentinvention with parallel port data output;

FIGS. 13A and 13B show a schematic block diagram of video processing ofanother embodiment of the present invention having parallel port dataoutput;

FIG. 14 is a diagrammatic view of an arrangement of the apparatus of thepresent invention for use with another workpiece thickness formula,where the workpiece is above the electromagnetic radiation source andbetween the ends of the electromagnetic radiation source; and

FIG. 15 is a diagrammatic view of an arrangement of the apparatus of thepresent invention for use with yet another workpiece thickness formulawhere the workpiece is above the electromagnetic radiation source andover one end of the electromagnetic radiation source.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

Referring now the drawings, and particularly FIG. 1, the apparatus ofthe present invention is represented at 20. For example purposes only,and not to be construed as limiting, the apparatus 20 is shown installedin a steel manufacturing facility wherein steel billets at very hightemperatures are within a process wherein they are guided along aconveyor line. Each outside edge of a billet 22 is monitored by tworeceivers 24 and 26. The billet 22 is shown as it moves along a conveyor60 having side supports 62 and 64, which support a plurality of conveyorrollers 66.

With the exception of a right-left reversal, the first receiver 24 ispreferably identical to the second receiver 26. The apparatus 20 alsoincludes an emitter 28 which comprises a housing 30 within which aresupported a linear array of discrete electromagnetic radiation sourcesconfigured to emit electromagnetic radiation preferably in the infraredregion of the electromagnetic spectrum. The electromagnetic radiationemission may be transmitted through a planar lens mounted within a slitor elongate opening 32. The housing 30 is preferably mounted so as toposition the slit 32 transversely to the direction of travel of thebillet 22 and at a location such that it extends from a locationunderneath the bottom surface of the billet 22 to a location positionedoutwardly from the bottom surface of the billet. A mounting member 34may be arranged to extend across the side supports 62, 64 to facilitatethe securement of the housing 30. In one embodiment of the presentinvention, the emitter 28 is located below the bottom surface of thebillet 22. However, in other arrangements of the present invention, theemitter 28 may be located either substantially directly adjacent thebottom surface of the billet or workpiece 22 or at varying distancesaway therefrom.

The first and second receivers 24, 26 are preferably mounted along abrace 68 that is supported by a post 70. The stand-off distance ordistance between the receivers 24, 26 and the conveyor 60 is preferablygreater than the distance from the conveyor to the emitter housing 30. Apassline is defined in the present invention as the plane through whichelectromagnetic radiation from the slit 32 impinges upon the bottomsurface of the workpiece 22 and is seen as it extends beyond the outsideedge thereof by one or more of the receivers. The receivers are thuswell away from possible destructive effects, such as heat, from theworkpiece 22.

The array of electromagnetic radiation emitting devices incorporatedwithin the emitter 28 will vary in length depending upon the applicationat hand. The accuracy of measurement achieved with the present inventionis enhanced as the density or number of electromagnetic radiationemitting devices per unit length of emitter 28 is increased. The spacingbetween each electromagnetic radiation emitting device 36 of emitter 28is preferably the same between each device 36. In one embodiment of thepresent invention a 0.1 inch center-to-center spacing between emittingdevices 36 is provided. The electromagnetic radiation emitting devices36 are preferably individually sequentially energized to emitelectromagnetic radiation in a predetermined scanning frequency. In oneembodiment of the present invention, one-half cycle of a 20 KHz clock orscanning frequency is incorporated. When the last device in such anarray has been energized and then cutoff, a reset signal is generated tobegin the sequence again at the first device 36 of the array 28. Thereset signal may be referred to as the "Sync Pulse". As the individualdevices 36 of the array 28 are energized in scanning fashion and theelectromagnetic radiation emitted progresses from a non-attenuatedoutside region or edge of the material being measured such as billet orworkpiece 22, a variation of the peak intensity of the emitted radiationfor this scan region will be witnessed at the associated receivers 24,26. This variation in attenuation results in the generation of a stairstep form of waveform which is preferably processed by low passfiltering to achieve a smooth curve. The midpoint of this curve ispreferably detected to evolve a time based trigger pulse which may beemployed by read out or control systems to determine the location of anoutside edge or the width of opposite edges of the workpiece 22.

Referring to FIGS. 2 and 3, internal structure of the receiverpreferably includes a housing 40 having an opening therein at 42. Theopening 42 is preferably aligned in parallel with the corresponding slit32 of the emitter 28 as seen in FIG. 1. A cylindrical gathering lens 44is placed in association with the opening 42. Above the lens 44, acircuit board 46 and a shield 48 are secured within the housing 40. Asupport board 50 is seen in FIG. 3 and preferably supports threerectangular silicon solar cells 51, 52, 53 in a linear array. The solarcells are preferably coupled in parallel. Each of the solar cells, inthis example, has a lengthwise extent of 2 centimeters and, thus,coupled in a grouping of three in the linear array as shown, the lengthof the photoresponsive components amounts to approximately 6centimeters. A filter 54 may be positioned over the entrances to thesedevices which confronts all electromagnetic radiation impinging thereonand passes only electromagnetic radiation or infrared radiation within aselected region of the electromagnetic spectrum.

Referring now to FIG. 4, the array of electromagnetic radiation emittingdevices 36 are represented generally at 80 behind the slit 32. Withinthe array 80, the scanning sequence may progress with the first of thedevices in the row. Complete emitters, receivers and associated hardwaremay be purchased from Harris Instrument Corporation in Columbus, Ohio.

Referring now to FIG. 5, an arrangement of the apparatus of the presentinvention is shown in which a workpiece 22 is shown in spacedrelationship apart from emitter 28. Positioned directly above a firstedge 90 of said emitter 28 is the first receiver 24. Positioned directlyover a second edge 92 of the emitter 28 is a second receiver 26.Electromagnetic radiation visible to receiver 26 at location R1 alongthe array 28, is the last diode to be visible by receiver 26 in a leftto right scan direction, before the next diodes are blocked from view ofreceiver 26 by the workpiece 22. Location R2 along the array is the lastdiode to be seen by receiver 24 before additional diodes are blockedfrom view by the workpiece. At an opposite end 29 of the workpiece, thediodes will once again become visible at location R3, to receiver 26. Atlocation R4 along the array the diodes will once again become visible toreceiver 24.

Referring to FIG. 6, the graph shows the transmitted electromagneticradiation video that begins at point R1 with receiver 26 and ends atpoint R4 with receiver 24. The spaces 94, 96 under the video plot inFIG. 6 represent the time between electromagnetic radiation emitteddiode sightings at receiver 26 and receiver 24 and is directlyproportional to the height of the workpiece edges above the emitter. Thetime during which the receivers produce different video signals can beused to measure height. The video signal from each receiver is comparedwith the video signal from the other receiver using an exclusive OR(XOR) logic circuit. This produces a logic one digital signal anytimeone receiver can see the array while the other receiver cannot. A singleXOR'ed video signal can be used to bring video information from bothreceivers to the measurement processing unit over one transmission line.A simple flip-flop circuit, such as illustrated in FIG. 7, can be usedto separate the video signal back into its original components, such asillustrated in FIG. 6. The conversion may be bi-passed when heightmeasurements are required. The signal processor may be used toalternately select width or height as required. Anytime one receiver cansee the array while the other receiver cannot, a logic 1 signal isproduced. This is electronically accomplished with an exclusive OR logiccircuit, for example, a CMOS 4030 IC. By processing the workpiece edge(with reference to the first edge encountered by the scanning LEDemitters) height above the array separately from the workpiece oppositeedge height (with reference to the second edge encountered by thescanning LED emitters) above the array, the tilt of the workpiece may beobtained when it is not in a plane parallel to the plane containing theemitter scan path. The average height that the workpiece is above theemitter may be obtained by determining the length between R2 and R1 andadding that value to the length between R4 and R3, then taking that sumand dividing it by 2. A video decoder arrangement for accomplishing thiscomputation is shown in FIG. 7.

FIG. 7 illustrates a block diagram of the circuit for separating thecombined exclusive OR (XOR'ed) video signal back into the two originalvideo signals from Receiver A and B. The system Sync Pulse that signalsthe end of one scan and the beginning of the next, is connected at point101 of the Video Decoder circuit. This positive pulse is applied to theRESET inputs of two sections 103, 105 of a CMOS 4013 flip-flop that arewired as bi-stable multivibrators. The Sync Pulse causes both flip-flopsto be reset, with the Q outputs at points 107 and 109 set to the logic 0state.

At the input terminal 111, the XOR'ed video signal is connected to aseries of two buffer inverter sections of a 4049 CMOS integratedcircuit. Each time the signal passes through a buffer/inverter stage thelogic polarity of the signal is inverted. The time T1 in the XOR'd videowaveform represents a positive transition. At point 113 in the circuit,this transition is inverted to negative, and therefore causes the firstnegative triggered one-shot multivibrator circuit 115 (NE558 IntegratedCircuit) to produce a brief positive pulse at point 117. This short(approximately 1 microsecond) pulse is connected to the clock input ofthe first flip-flop where it will cause the Q output at point 107 tochange to the logic 1 state. At time T3 the inverted input waveform willagain produce a negative transition at point 113. The resulting one-shotpulse will again cause a state change in the first flip-flop, returningthe Q output at point 107 to logic 0. The waveform produced at point 107is identical to the original video signal from Receiver 26 asillustrated in FIG. 6.

The second one-shot input at point 119 will have a positive transitionat times Ti and T3 because of the second buffer/inverter stage in serieswith it. Because it is negative triggered, however, the second one-shotmultivibrator 121 will not produce an output pulse until T2 and again atT4. The waveform produced by the second flip-flop Q output at point 109is identical to the original video signal from receiver 24 in FIG. 6.

Referring now to FIG. 8, a single edge position formula may be used inassociation with data collected from the apparatus of the presentinvention. In this embodiment, x represents the distance along theworkpiece 22 from a far right end of the workpiece to a point on a lineextending directly below receiver 24 and forming a 90° angle with theworkpiece. The distance from the receiver to the workpiece is designatedby the letter L. The distance from receiver 26 to the emitter 28 isdesignated by the letter H. The width of the electromagnetic radiationemitting diode scan is designated by the letter W. Point R1 along theemitter is the first location in which electromagnetic radiation isvisible to receiver 24 in a left to right scan direction. Location R2 atthe emitter, is the first location at which electromagnetic radiation isvisible to receiver 26. The following formulas may then be invoked:##EQU1##

Referring to FIG. 9, the height S at which the workpiece is positionedabove the emitter may be computed. In this Figure the locations R1 andR2 are the same as defined in FIG. 8. The distances H and W also remainthe same. The following formulas would then apply: ##EQU2##

Referring now to FIG. 10, an electrical schematic of one embodiment of aprocessor of the present invention is shown. The circuit illustrated inFIG. 10, represents the circuit blocks labeled Video Pre-processor 131and Video Select Switch 133 in FIG. 12. The circuits in FIGS. 10 and 12are used to connect a binocular SCAN-A-LINE® sensor to olderSCAN-A-LINE® measurement processing systems. If there is significantmovement of the product being measured during the time of three scans,the measurement data taken will be inaccurate. The circuit is stilluseful in that it provides compatibility with older equipment.

The IC's labeled 135 are CMOS buffer/inverter sections from a 4049integrated circuit. They are used to invert the logic state of digitalsignals in the circuit.

The IC's labeled 137 are CMOS 4066 analog switches. These are used toselect input and output signals. A logic 1 at the control inputelectrically connects the CMOS switch input and output.

The 4013 CMOS integrated circuit 139 is a bi-stable multivibrator(flip-flop). A positive transition at the clock input transfers thelogic signal at the D input 141 to the Q output 143.

The NE558 at 145 is a negative triggered one-shot multivibrator. When anegative going transition is sensed at the input, the NE558 produces apulse at the output. The length of the output pulse is determined by theresistor and capacitor at the timing input of the circuit.

The Sync Pulse that signals the end of one scan and the beginning ofanother is connected to a 4049 inverter at node 148. The inverted SyncPulse at node 149 of the 4049 is connected to node 150, the input of theNE558 where it triggers the one-shot multivibrator to produce a positiveoutput pulse slightly longer than the Sync Pulse. The length of thepulse produced is determined by the 4.7k resistor 151 and the 0.1 μFcapacitor 153. This pulse from node 155 of the NE558 is connected to theRESET input of the 4013 flip-flop at node 146. The RESET input pulsecauses the Q output at node 157 to go to logic 0 at the end of eachscan.

The VIDEO IN signal 159 is the XOR video signal from FIG. 6. Itrepresents a composite of the video signals from Receiver 24 andReceiver 26. The VIDEO IN signal is inverted in the 4049 from node 161to node 163. It is again inverted in the 4049 at 136 from node 165 tonode 167. The signal at node 167 has the same logic polarity as theVIDEO IN signal and is connected to node 175, one input of a 4066 CMOSswitch. The signal at node 165 is the inverted logic state of VIDEO IN159 and is connected to node 177, the input of another 4066 CMOS switch.When the A/B select input signal 179 is at logic 1, node 177, thecontrol input of the 4066 is connected via the CMOS switch to node 181.

Because the logic is inverted from node 171 to node 173 of the 4049,node 13 of the 4066 is at logic 0 and node 175 is not connected to node183 via the CMOS switch. In this state the inverted VIDEO IN signal isconnected via the CMOS switch to the node 185 input of the NE558one-shot 145. Every time the VIDEO IN signal transitions from logic 0 tologic I a pulse is produced by the NE558 at node 187. The pulse outputfrom node 187 of the NE558 is connected to the clock input of the 4013at node 189. Each time a clock pulse transitions to logic 1, the 4013 Qoutput at node 157 changes state. In the A selected mode, the output ofthe 4013 flip-flop 139 at node 157 is the Video A signal.

If the A/B input 179 is switched to logic 0, the non-inverted VIDEO IN159 signal would be sent to the NE558 via the 4066 CMOS switch nodes 175and 183. The NE558 at 145 would not produce pulses at the oppositetransition times causing the 4013 output at node 157 to be the Video Bsignal.

The Video A or Video B signal from node 157 of the 4013 flip-flop isconnected in node 191 of a 4066 CMOS switch. If the H/W height or width)select input 193 is at logic 1, the Video A or Video B width signal fromthe 4013 node 157 is connected to the Video Out 201 via a 4049buffer/inverter node 195. If a logic 0 signal is connected to the H/Winput, the XOR video and VIDEO IN 159 is connected to the Video Out 201through the 4066 node 197 and node 199.

Referring now to FIG. 11, a workpiece of a certain thickness is conveyedover an emitter 28. In this arrangement of the present invention theletter T is representative of the thickness of the workpiece. Thelocation R1 is of the same definition as supplied in previous figures,while location R2 is electromagnetic radiation different in thisarrangement. Due to the fact that the workpiece has substantialthickness the receiver 26 is blocked from receiving electromagneticradiation from the emitter to a greater extent than with a thinnerworkpiece. Otherwise, R2 remains the first location at whichelectromagnetic radiation is received by receiver 26 in a left to rightscan direction. Also shown in FIG. 11 are locations A, B, and C.Location A is the center of receiver 24. Location B is the first edge 90of emitter 28 and location C is the upper, right corner of theworkpiece. The following formulas would apply to compute the thicknessof the workpiece: ##EQU3##

The measured width of a workpiece can be taken from either receivers'view of the array. With compensation for the height of the workpiece asdescribed above, the measured width of the workpiece is proportional tothe time during which receiver 24 cannot see the array. The measuredwidth is also proportional to the time during which receiver 26 cannotsee the array. The most accurate width measurement can be made byaveraging the measurements as seen by both receivers. In addition tobetter average, this method can be used to compensate for the workpiecebeing in a non-parallel plane. If the plane of the workpiece is tippedat an angle to the plane of the emitter array, one receiver will see thewidth as wider than it is, while the other will see a narrower widththan normal. The average of these two measurements is the correct actualwidth of the measured object. A block diagram of one mode of videoprocessing of the signals generated by the present invention is shown inFIG. 12.

FIG. 12 illustrates a block diagram of one method for producing aparallel digital output for Video A 203, Video B 205 and XOR Video 207.The represented circuit produces a 12 bit binary output 209 with amagnitude representing the selected video signal. The VideoPre-Processor 131 and Video Select Switch 133 sections of the diagramare described in more detail in FIG. 10 and the accompanying descriptionof that Figure.

The Sync Pulse 211 that signals the end of one scan and the beginning ofthe next, is connected to the negative triggered input of an NE558one-shot multivibrator 212. The Sync Pulse is also connected through a4049 buffer/inverter 213 to another NE558 one-shot input 215. The secondone-shot 215 produces the Latch (Store Counter) pulse 217 at the leadingedge of the Sync Pulse. The first (non-inverted input) one-shot 212produces the Reset Counter pulse 219 at the trailing edge of the SyncPulse.

The Video signal selected by the Video Sel Switch circuit (see FIG. 10)is fed to one input of a 2 input NAND gate 221. The other input of theNAND gate is connected to a 200 kHz. crystal oscillator 223. Wheneverthe video signal from the Video Select Switch is at logic 1 the 200 kHz.clock pulses are inverted and sent to the gate output 225. Any time thevideo signal is at logic 0 the gate output will be logic 1 with no clockpulses present.

The gate output is connected to a 12 bit binary counter 227. The counteris reset at the trailing edge of the Sync Pulse with the pulse 219generated in the NE558 as described above. During the following scan,the counter counts all the clock pulses present while the selected videosignal is at logic 1. On the leading edge of the Sync Pulse the StoreCounter Pulse latches the counter output into a 12 bit latch circuit229.

The 12 bit latch output can be read by a computer or microprocessorparallel input port any time during the following scan, while new datais being generated in the 12 bit binary counter 227. The computer can beused to select the video mode required and to alternate between Video A,Video B and XOR Video to collect data for binocular SCAN-A-LINE®calculations. FIG. 13A and 13B show a preferred embodiment of thepresent invention for parallel processing of binocular video signals,which is analogous to FIG. 12 as described above.

As mentioned above, the sequential processing of the Video A, Video Band XOR Video signals can lead to problems if the material beingmeasured moves during the scans required to read in the measurementdata. To overcome this problem, the XOR Video signal can be processed asin FIG. 13. With all three Video signals present at the output of thiscircuit, it is possible to gate the 200 kHz. clock pulses to three 12bit counters 231, 233, 235 independently. The outputs of these counterscan be stored in three separate 12 bit latches 237, 239, 241. IfTri-State outputs are available on these latches as in the 74LS573 IC,the computer can select which latch to read and easily read all threevideo counts into memory while the following scan is progressing. Thismethod represents the preferred method for Binocular SCAN-A-LINE® signalprocessing.

A somewhat lower cost measurement processing system can be designedaround three 12 bit buffered digital to analog converters. In thismethod, the three counter outputs are stored in the latches providedwithin the digital to analog converter integrated circuits. Theresulting analog outputs represent the three video signals as in thedigital method. This analog method has some advantages where themeasurement signal is used with analog input strip guiding or steeringsystems.

Referring to FIG. 14, another arrangement for use with the presentinvention is shown in which processing of the gathered signalinformation can result in computation of workpiece width, thickness, andheight above the emitter array. The letter designations R1, R2, R3, R4,H, T, S, and W are the same as described above in other embodiments.Location A is representative of the point in space where the upper leftcorner of the workpiece resides at any moment in time. The letter B isrepresentative of the point and space at which the lower left corner ofthe workpiece resides. The letter C is representative of the point inspace at which the upper right corner of the workpiece resides at anygiven time. The letter D is representative of the point in space atwhich the lower right corner of the workpiece resides. The letter K isrepresentative of the point in space directly horizontal from point Aand along the line of vertical cite of receiver 24 with the left edge ofthe emitter 28. The letter E is representative of the point in spacedirectly horizontal from point B and in the same vertical line as pointK. The letter G is representative of the point in space directlyhorizontal from the letter C and in the vertical line of cite ofreceiver 26 with the right edge of emitter 28. The letter F isrepresentative of the point in space directly horizontal from point Dand in the same vertical line as point G. With this arrangement, thefollowing formulas apply: ##EQU4##

Referring to FIG. 15, a electromagnetic radiation different arrangementis shown in which the workpiece has one edge that extends beyond thevertical emitance of the emitter array 28 and the opposite edgeterminating at some point between the first and second edges 90, 92 ofthe emitter 28. The letter designation have all been defined above withthe exception of the letter X. The letter X is indicative of thehorizontal location along the emitter 28 which is directly verticallydistanced below the right edge of the workpiece. By computing X, thethickness can be determined for the workpiece as set forth in thefollowing formula: ##EQU5##

When a measurement is required for an object wider than the longestarray available, two scanned arrays, each with a set of at least tworeceivers can be used. The arrays are preferably mounted with thebeginning LEDs in the array toward the center of the workpiece with onearray positioned under each edge of the workpiece to be measured. As thescan begins, the LEDs in both arrays are hidden from all four receivers.As the scan progresses, one of the two outside receivers will first seeelectromagnetic radiation from a LED because it can see electromagneticradiation under the workpiece. If the workpiece is perfectly centered,the two outside receivers will see LED electromagnetic radiation atexactly the same time. At some point in time later in the scan, thereceivers located interiorly over the arrays, will also see LEDelectromagnetic radiation. The greater the distance from the array tothe workpiece, the greater will be the difference in view times for eachedge.

In this arrangement, the width of the workpiece is again proportional tothe total scan time during which the array is hidden from the receiverswith a compensation factor for height as computed from the timedifference on each edge. In addition, there is a constant offset to beadded to the width calculation to allow for the separation between theends of the arrays.

The present invention, as described above is susceptible to variouschanges and modifications that are fully intended to fall within thescope of the subjoined claims.

What is claimed is:
 1. A measurement apparatus, comprising:an array ofdiscrete electromagnetic radiation emitting devices, said array locateda distance from a first surface of a material workpiece, and extendingpartially outwardly from an edge of said workpiece, each of said devicesbeing responsive to the application of current thereto to emitradiation; a first receiver responsive to radiation emitting from saiddevices, said first receiver located a stand-off distance from a secondsurface of said material workpiece; a second receiver responsive toradiation emitting from said devices and located a stand-off distancefrom said second surface of said workpiece; a drive circuit for applyingsaid current to said discrete radiation emitting devices forsequentially actuating each of said emitting devices of said array; aprocessor for receiving first receiver signals from said first receiverand for receiving second receiver signals from said second receiver,said processor adapted to process said first receiver signals withrespect to said second receiver signals; and wherein said first receiversignals and said second receiver signals are used to calculatemeasurements of said workpiece.
 2. A method of measurement, comprisingthe steps of:positioning an array of electromagnetic radiation emittingdevices a distance from a first surface of a material workpiece, suchthat said array extends partially outwardly from an edge of saidworkpiece; positioning a first electromagnetic radiation receiver astand-off distance from a second surface of said material workpiece,said first receiver responsive to said electromagnetic radiation emittedfrom said emitting devices; positioning a second electromagneticradiation receiver a stand-off distance from said second surface of saidmaterial workpiece, said second receiver responsive to saidelectromagnetic radiation emitted from said emitting devices;sequentially actuating each of said emitting devices of said array ofemitting devices; and processing signals received from said firstreceiver with respect to signals received from said second receiver toarrive at said measurement.
 3. The method of claim 2, wherein saidmeasurement information is self-calibrating.
 4. The method of claim 2,wherein said array is sequentially energized beginning with a firstemitting device and each emitting device in a row after said firstemitting device is subsequently energized until a last emitting deviceis energized, and the energization of the row of emitting devices isbegun again.
 5. The method of claim 2, wherein said first receiver ispositioned directly vertically above a first emitting device in saidarray.
 6. The method of claim 5, wherein said second receiver ispositioned directly vertically above a last emitting device in saidarray.
 7. The method of claim 2, wherein said patterns are righttriangles formed by one of said receivers, an emitting device at one endof said array, and an emitting device not blocked by said workpiece andfirst visible to said one of said receivers.
 8. The apparatus of claim1, wherein the processor uses an exclusive OR circuit to permit thesimultaneous transmission of two edge positioned video signals over onesignal line.